The present invention relates to the field of medical devices, in particular therapeutic intervention devices for the reduction of edema and improvement of venous return to the heart with applications in the field of medicine.
Prior to the present invention, various compression devices have been known in the art for applying compressive pressure to a patient's limbs in order to increase blood flow and return of fluid from a limb.
These compression devices take a number of different forms, including:                1) The SCD (trademark of The Kendall Company), a sequential compression device that provides intermittent pulses of compressed air that sequentially inflate multiple chambers in a sleeve, beginning at the ankle and moving up the leg. This results in a wave-like milking action that empties the veins and results in greatly increased peak blood flow velocity, thus providing a non-invasive method of prophylaxis to reduce the incidence of deep vein thrombosis (DVT). Patients with edema (swelling of the extremity) can develop tissue breakdown (venous stasis ulcer). It has also been shown that pneumatic compression can be highly effective in the treatment of edema and venous ulcers.        2) Non-elastic therapeutic compression band by band, with the user capable of tightening the compression bands to control the non-elastic pressure. This form of cyclical or sequential compression of limbs improves blood fluid returns for reducing edema and can improve healing.        3) Devices that are intended to apply and remove pressure from at least a portion of the patient's extremity. For example, a patient's legs may be enclosed in air bags that may be inflated to apply pressure on the leg and deflated to remove pressure from the leg. Synchronous application of pressure on an extremity can enhance the flow of blood into the extremity, as well as enhancing the pumping of blood through the heart.        4) They function by applying pneumatic compression sequentially and in gradient levels from ankle to thigh for a predetermined time, e.g. 15 seconds, followed by a period of time, e.g. 45 seconds, when no pressure is applied. The particular time period selected is chosen to be optimum for pushing venous blood out of the leg (during the compression cycle) and to allow arterial blood to refill the leg (during the decompression interval).        
Evidence suggests that it may also be advantageous to apply pneumatic compression to the foot to provide significant venous blood movement therefrom. For example, U.S. Pat. No. 4,702,232 and a division thereof, U.S. Pat. No. 4,841,956, of Arthur M. N. Gardner and Roger H. Fox relate to a device for inducing venous-return flow, which device is intended for use on an impaired human leg. In accordance with the teachings of these patents, the cyclical succession of venous pump action which would occur in normal walking is achieved by involuntarily or artificially activating a foot pump followed by artificially induced separate transient operation of a proximal calf pump and then an artificially induced separate operation of a distal calf pump. As disclosed, the pump actions are achieved by providing inflatable bags or cuffs around the foot and upper and lower calf regions, the inflatable cuffs being separately connected by tubes to a fluid pressure supply means. Each cuff is inflated and then deflated before the next cuff is inflated. Moreover, the cuffs are not inflated sequentially from distal to proximal, e.g. the sequence disclosed in the patent of foot pump, proximal calf pump and then distal calf pump which procedure does not encourage an effective pumping of blood from the leg.
In a related area of intervention, devices for prosthetic limbs have been developed to create hypobarically controlled artificial limbs for amputees and methods for preventing loss of residual limb volume due to weight-bearing pressures. An amputee is a person who has lost part of an extremity or limb such as a leg or arm that commonly may be termed as a residual limb. Residual limbs come in various sizes and shapes with respect to the stump. That is, most new amputations are either slightly bulbous or cylindrical in shape while older amputations that may have had a lot of atrophy are generally more conical in shape. Residual limbs may further be characterized by their various individual problems or configurations including the volume and shape of a stump and possible scar, skin graft, bony prominence, uneven limb volume, neuroma, pain, edema or soft tissue configurations.
Devices have been developed to employ negative pressure in a closed chamber in the form of a socket is donned by pulling in with a stocking, pulling the stocking out of the socket and then closing the opening with a valve. This creates a seal at the bottom and the stump is held into the socket by the hypobaric seal.
Older appliances that employed negative pressure involved an open-ended socket, meaning there was an air chamber in the bottom of the socket. These did not work particularly well because they would cause swelling of the residual limb into the chamber created by the negative draw of suspending the weight of the leg and being under a confined area. This would lead to significance edema that would be severe enough to cause stump breakdown and drainage. It was later discovered that total contact was essential between the residual limb and the socket and once you had total contact the weight was distributed evenly or the suspension was distributed over the whole surface of the limb rather than just over the open chamber portion of the socket.
The human body as a whole is under approximately one atmosphere of pressure at sea level. It keeps and maintains a normal fluid appliance throughout the body. When an amputee dons prosthesis and begins taking the pressures of transmitting the weight of the body through the surface area of the residual limb to the bone, there is increased pressure on the residual limb equal to one atmosphere plus whatever additional pressures are created by weight bearing. This increased pressure causes the eventual loss of fluids within the residual limb to the larger portion of the body that is under less pressure. This loss of fluids causes the volume of the residual limb to decrease during the day. It varies from amputee to amputee, but it is a constant among all amputees, the more “fleshy”, and the softer the residual limb, the more volume fluctuation there will be. The greater the weight and the smaller the surface area, the greater the pressures will be and the more “swings” there will be in fluids. In the past, the amputee had to compensate for this volume decrease by removing the artificial limb and donning additional stump stockings to make up for the decreased residual limb volume.
It has been found that it is essentially impossible to maintain a perfect, airtight seal between the residual limb and the sockets disclosed in U.S. Pat. No. 5,549,709, with the result that slow air leakage into the sockets diminishes the vacuum in the sockets. With the reduction in vacuum, the beneficial effects of the vacuum also slowly diminish. Consequently, there is a need for a means for maintaining the vacuum in the socket cavity in the presence of some air leakage past the seal.
A related device in U.S. Pat. No. 6,551,280 has described using vacuum assisted compression to provide support or pressure to tissue for wound healing. Lockwood et al. in U.S. Pat. No. 6,752,794 describe a similar device for the delivery of negative pressure to a wound for the purpose of wound healing. These devices are intended to contain a material that is capable of being contracted from its relaxed state to an evacuated state. The material applies pressure to the tissue of a patient when the material is in its relaxed state. Reduction of pressure by application of a vacuum results in a contracted state of the device, so that the device can be applied or delivered to a patient. Release of vacuum results in a return to the relaxed state, thus providing a maximum desirable pressure to tissue and avoiding the possibility of over-pressure that can result in tissue damage or necrosis. The description of these devices does not contemplate the use of self-powered creation and maintenance of negative pressure for edema control with ambulation. Nor does the descriptions, or any other in prior art, contemplate the use of circumferentially applied vacuum which will be crucial to the simultaneous treatment of fluid accumulations (i.e. leg edema) and skin wounds as found in both diabetes and chronic venous insufficiency.
Additionally, Vogel et al. in U.S. Pat. No. 6,135,116 contemplated a method and apparatus for providing concurrent applications of intermittent pneumatic compression therapy and vacuum assisted closure for the treatment of wounds. This patent describes the use of “a wound dressing for introduction of a negative pressure into a wound on a patient's foot and a foot wrap for application of positive, compressive forces to substantially all of the patients foot.” While this patent references the use of a “wrap” the authors very specifically describe a wrap that is akin to existing intermittent positive pressure compression devices. The novelty of the patent relates, then, to the combination of these treatments. Significantly, the authors do not contemplate the use of a wrap for the delivery of negative pressure compression to an entire foot or limb.
The limitations of existing delivery systems for negative pressure wound therapy are significant and are well described in the medical literature. The Vacuum-Assisted Closure (VAC) device employs the application of foam and layers of dressing locally over a wound surface. This and related devices are limited in that: 1) Use generally requires that patients and families be willing to sleep, ambulate, and rest during the day with the device in place, 2) Weight-bearing while using the VAC is generally considered to be dangerous to patient, 3) Nearly 20% of individuals with smaller forefoot or midfoot wounds fail VAC treatment, and 4) Applications of the VAC system are not intended for small wounds or for the prevention of skin wounds. In addition, VAC is applied locally and due to the complex layering of foam and dressing of the wound, has not been applied circumferentially as is the case with the present invention.
To our knowledge, the use of a device that employs total contact with a non-amputated limb by creating and maintaining (through the use of mobility and weight bearing) a negative pressure vacuum for the control of edema has not been contemplated in the prior art. Devices have utilized positive pressure compression in various forms to facilitate the return of interstitial fluid (or edema) from limbs to the heart. Other devices have been designed to use a negative pressure vacuum to improve swelling, protect skin, and provide a means for suspension in amputated limbs.
In addition, the use of a circumferential wrap for a limb in the delivery of negative pressure for the purposes of wound healing/prevention/edema control has not been contemplated in the prior art.
The innovation of present invention involves the use of a flexible stocking-type device that is employed circumferentially around a limb and employs the creation and maintenance of negative pressure to reduce edema, improve venous return, and help protect skin.